System for guiding trailer along target route during reversing maneuver

ABSTRACT

The present invention relates to a vehicle control system ( 1 ) for controlling a vehicle ( 3 ) to facilitate reversing a trailer ( 5 ) coupled to the vehicle ( 3 ). The vehicle control system includes a processor ( 33 ) configured to receive a target trailer destination (D TAR ). The current position of the trailer ( 5 ) is determined by the processor ( 33 ). A target route (R) is then modelled to guide the trailer ( 5 ) from its current position to the target trailer destination (D TAR ). The processor ( 33 ) is configured to output a vehicle control signal to control the vehicle ( 3 ) to guide the trailer ( 5 ) along the target route (R). The invention also relates to a method of controlling a vehicle ( 3 ) to facilitate reversing a trailer ( 5 ).

RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application of PCTApplication No. PCT/EP2014/064270, filed on Jul. 3, 2014, which claimspriority from Great Britain Patent Application No. 1312040.7 filed onJul. 4, 2013, the contents of which are incorporated herein by referencein their entireties. The above-referenced PCT International Applicationwas published in the English language as International Publication No.WO 2015/001066 A9 on Jan. 8, 2015.

TECHNICAL FIELD

The present disclosure relates to a vehicle control system; a vehicle;and a method of controlling a vehicle.

BACKGROUND OF THE INVENTION

It is known from GB 2447672 to provide a computing unit to calculate ahitch angle between a trailer and a vehicle. The computing unit usesimage data from three video cameras, fitted respectively to the rear ofthe vehicle and one on each door mirror, to track the position of atrailer-mounted marker to determine the position of the trailer relativeto the vehicle. The computing unit can also predict a trailer targetroute and this is output to the driver on a display as guide linesoverlaid onto a camera view.

At least in certain embodiments, the present invention relates to animproved control system.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a system, a vehicle and amethod as claimed in the appended claims.

According to a further aspect of the present invention there is provideda vehicle control system for controlling a vehicle to facilitatereversing a trailer coupled to the vehicle, the vehicle control systemcomprising a processor configured to:

-   -   receive a target trailer destination;    -   determine a current trailer position ; and    -   model a target route from the current trailer position to the        target trailer destination;    -   wherein the processor is configured to output a vehicle control        signal for controlling the vehicle to guide the trailer along        the target route. The target trailer destination may be        spatially displaced from the current trailer position and the        controller may be operative to guide the trailer from its        current position to the target destination. The target route may        be modelled to enable the trailer to be reversed from the        current trailer position to the target trailer destination.        Rather than directly control the direction of travel of the        vehicle or the trailer, the user may specify the target        destination for the trailer and the processor may be configured        to generate a target route. In particular, the processor may be        configured to model the target route for the trailer to follow        as it travels from its current position to the specified target        destination.

The vehicle control signal can define the required steering angle inputsfor the vehicle to guide the trailer along the target route. These couldbe output, for example to an audio or visual system, to prompt the userto make appropriate changes to the steering angle. Alternatively, thevehicle control signal can be output to steering control means forcontrolling the steering angle. The steering control means can, forexample, comprise electronic power assisted steering (EPAS).

The current trailer position can define a current hitch angle (betweenthe vehicle and the trailer) which determines an actual travel directionof the trailer. The current trailer position can be determined based onone or more sensor signals. The current trailer position can be measuredby one or more sensors, such as a rotary sensor, provided at thecoupling between the vehicle and the trailer for measuring a hitch angleof the trailer. The current trailer position could be determined bymeasuring the orientation of the trailer in relation to the vehicle, forexample employing one or more ultrasonic sensors or one or more imagesensors (for example disposed in a camera). The image data generated bysaid one or more image sensors could be analyzed to track the trailer,for example by identifying a feature of the trailer and/or a targetprovided on the trailer.

The target trailer destination can comprise position (i.e. spatial)data; and/or orientation (i.e. angular) data. The processor candetermine the spatial and/or angular relationship between the currenttrailer position and the target trailer destination.

The target route can comprise one or more curves; and/or one or morelinear sections. The target route can comprise only one reversingmovement; or can comprise a sequence of forward and reversing movements.The user could specify whether a single reversing movement or multiplereversing movements are performed. The processor could be configured tooutput braking signals and/or acceleration signals for controlling thebraking and acceleration respectively of the vehicle. Alternatively, thedriver of the vehicle can control one or both of vehicle accelerationand braking. The processor can be configured to output driver prompts,for example to perform one or more of the following functions:accelerate, decelerate, change gear (such as select Drive or Reverse),engage parking brake and so on. The processor could be configured toinhibit the maximum speed of the vehicle, for example to 10 km/h.

The vehicle control signal can map a center point of the trailer to thetarget route. The vehicle control signal can be generated to maintainthe center point of the trailer substantially coincident with the targetroute.

The target route can define a target trailer travel direction at eachpoint along its length. The processor can be configured to control thevehicle to match the actual trailer travel direction to the targettrailer travel direction as it travels along the target route. Thevehicle control signal can control the steering angle of the vehicle tomaintain the actual trailer travel direction at least substantiallycoincident with the target trailer travel direction. The actual trailertravel direction can thereby match the target trailer travel direction.

The processor can be configured to identify permissible target trailerdestinations. The permissible target trailer destinations could be basedon the identification of one or more obstructions. The processor can beconfigured to identify said permissible target trailer destinationsbased on one or more of the following: a maximum permissible hitchangle; the detected space available for the trailer and/or the vehicle;a detected terrain parameter (such as an incline or gradient). Theprocessor can be configured to inhibit selection of an impermissibletarget trailer destination.

The processor can be configured to receive image data from one or morevideo cameras disposed on the vehicle and/or the trailer. The processorcan comprise an image processing module for identifying obstruction(s)in video image data obtained from one or more optical cameras. The imageprocessing module can be configured to identify one or more obstructionsproximal to the trailer and/or the vehicle. Alternatively, or inaddition, ultrasonic and/or laser sensor systems could be provided fordetecting said obstruction(s). The processor could be configureddynamically to modify the target route if an obstruction is identified.

The processor could be configured to determine if there is sufficientspace available to manoeuvre the trailer to the target trailerdestination. Based on predefined trailer parameters (such as the trailerlength, width and axle location), the processor can calculate a routecorridor required to reverse the trailer. The imaging system can thenidentify obstacles proximal to the vehicle and/or the trailer anddetermine if there is sufficient space available to reverse the trailer.The processor can be configured to modify the target route of thetrailer to remain within the calculated route corridor.

The processor can be configured to output the target trailer destinationand/or the target route to a display. The target trailer destinationand/or the target route could, for example, be overlaid onto a videoimage from one or more of said video camera(s).

The target trailer destination can be specified by a user. A humanmachine interface can be provided for specifying the target trailerdestination. The human machine interface can, for example, comprise adisplay device, such as an LCD screen. An input means can be providedfor the human machine interface. The input means can, for example,comprise one or more of the following: a touchscreen, a capacitivesensor, a joystick, a rotary wheel, a trackball, voice recognition,gesture recognition, and eye tracking. A graphical image can bedisplayed on the display device to represent the target trailerdestination. The position and/or the orientation of the graphical imagecan be controlled using the input means. The position and/or theorientation of the graphical image can be converted to data to identifysaid target trailer destination and output to the processor.

A scaling function can be applied to the graphical image as it is movedaround the screen. The scaling function has particular application whenthe graphical image is displayed in a perspective view, for example asan overlay onto a video image from a camera disposed on the vehicle orthe trailer.

The graphical image can represent a footprint of the trailer, forexample representing an outline of the trailer on the ground. Thegraphical image could, for example, comprise a rectangle. Alternatively,the graphical image could provide a 3-dimensional representation of thetrailer, for example a vector image or a rendering of the trailer. Thegraphical image can provide a scale representation of the trailer.

The vehicle control signal can comprise a steering control signal forcontrolling a steering angle of the vehicle.

According to a still further aspect of the present invention there isprovided a vehicle control system for controlling a vehicle tofacilitate reversing a trailer coupled to the vehicle, the vehiclecontrol system comprising a processor configured to:

-   -   generate a target route from the current trailer position to the        target trailer destination;    -   wherein the processor is configured to generate the target route        by modifying a pre-defined path based on a determined angular        offset and/or positional offset between the current trailer        position and the target trailer destination.

The pre-defined path can comprise first and second curves. The first andsecond curves can be arranged in an S-shape. The processor can beconfigured to increase or decrease an included angle of one or both ofsaid first and second curves in dependence on said angular offset. Theprocessor can be configured to define a minimum radius of curvature inthe target route based on a jack-knife angle of the trailer.

According to a further aspect of the present invention there is provideda vehicle comprising a vehicle control system of the type describedherein.

According to a still further aspect of the present invention there isprovided a method of controlling a vehicle to reverse a trailer to aspecified target trailer destination, the method comprising:

-   -   receiving an input to define a target trailer destination;    -   determining a current trailer position;    -   modelling a target route from the current trailer position to        the target trailer destination; and    -   outputting a vehicle control signal for controlling the vehicle        to guide the trailer along the target route.

According to a yet further aspect of the present invention there isprovided a method of generating a target route for reversing a trailerfrom a current position to a target destination; the method comprising:

-   -   modifying a pre-defined path based on a determined angular        offset and/or positional offset between the current position and        the target destination to generate the target route. The        pre-defined path can be stored in memory. The pre-defined path        can, for example, comprise first and second curves, for example        arranged in an S-shape. The method can comprise applying a        minimum radius of curvature to the target route, the minimum        radius of curvature being based on the jack-knife angle of the        trailer.

The methods described herein can each be computer-implemented, forexample on a computational apparatus comprising one or moremicroprocessors. According to a yet further aspect of the presentinvention there is provided a computer program product comprising acomputer readable storage medium including computer readable programcode, where the computer readable program code when executed on acomputer causes the computer to perform the method(s) described herein.

The term processor used herein is to be understood as covering bothsingle processors and multiple processors.

Within the scope of this application it is expressly envisaged that thevarious aspects, embodiments, examples and alternatives set out in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings, and in particular the individual features thereof, may betaken independently or in any combination. Features described inconnection with one embodiment are applicable to all embodiments, unlesssuch features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way ofexample only, with reference to the accompanying figures, in which:

FIG. 1 shows a plan view of a trailer coupled to a vehicle incorporatinga vehicle control system in accordance with an embodiment of the presentinvention;

FIG. 2 shows a schematic representation of the vehicle and the controlsystem in accordance with an embodiment of the present invention;

FIG. 3 shows a plan view of the vehicle and trailer with the targettrailer destination and the target route indicated;

FIG. 4 shows a plan view of the vehicle and trailer shown in FIG. 3 withthe path to be followed by the wheels of the trailer indicated;

FIG. 5 illustrates the routes traced by the rotational centers of thevehicle and the trailer and the trailer hitch;

FIGS. 6A-6E illustrate the generation of the target route in differentscenarios;

FIGS. 7A and 7B illustrate the control strategy for guiding the traileralong the target route;

FIG. 8 illustrates the vehicle and trailer dimensions and associatednomenclature; and

FIG. 9 shows a display image from the rear camera on the trailer with atarget trailer destination indicated.

DETAILED DESCRIPTION OF AN EMBODIMENT

A vehicle control system 1 for assisting with the reversing of a vehicle3 and a trailer 5 in accordance with an aspect of the present inventionwill now be described with reference to FIGS. 1 to 9.

The vehicle control system is operable to facilitate reversing of thetrailer 5 when it is coupled to the vehicle 3 (the combination of thevehicle 3 and the trailer 5 can be referred to as ‘a rig’). Morespecifically, the vehicle control system 1 is configured to control thesteering of the vehicle 3 such that the trailer 5 is reversed to atarget trailer destination D_(TAR) specified by the user. In the presentembodiment, the operation of the throttle and brakes of the vehicle 3are controlled by the user, but these control functions could beautomated.

A plan view of the vehicle 3 and the trailer 5 is shown in FIG. 1. Thevehicle 3 has two front wheels W1, W2 and two rear wheels W3, 4. Asillustrated in FIG. 2, the front wheels W1, W2 of the vehicle 3 aresteerable in conventional manner to define a steering angle θ. Thetrailer 5 has two wheels TW1, TW2 which are not steerable.

As shown in FIGS. 1 and 2, the vehicle 3 is provided with a vehicleimaging system comprising a centrally mounted rear vehicle camera 9; andleft and right side vehicle cameras 10, 11 mounted in respective wingmirrors 13, 15. The vehicle cameras 9, 10, 11 are optical camerasarranged to face to the rear of the vehicle 3 and their fields of viewV1, V2, V3 are illustrated by dashed triangles. The vehicle 3 optionallyalso comprises an obstruction detection system, for example side radarsystems 7A, 7B for detecting the presence of an obstruction in the rearthree quarters position of the vehicle 3.

A tow hitch 17 is mounted to the vehicle 3 for coupling to a trailercoupling 19 mounted to the trailer 5. The tow hitch 17 is an upwardlyprojecting tow ball in the present embodiment. The trailer coupling 19is mounted to a hitch frame 21 disposed at the front of the trailer 5.In the present embodiment, the hitch frame 21 is an A-frame having afront apex 23 to which the trailer coupling 19 is mounted. A target 25is mounted to a front face 27 of the trailer 5 to enable the position ofthe trailer 5 relative to the vehicle 3 to be determined, as describedherein. The target 25 is a visible image comprising three circlesarranged in a triangular formation. It will be appreciated that thepresent invention can be implemented with other targets 25, for examplecomprising different symbols/images or non-visible targets.

The trailer 5 is provided with a trailer imaging system comprising acentrally mounted rear trailer camera 29; and left and right sidetrailer cameras 30, 31 mounted on respective sides of the trailer 5. Thetrailer cameras 29, 30, 31 are optical cameras arranged to provide videoimages of the area around the trailer 5 which may otherwise be obscuredfrom view. The fields of view TV1, TV2, TV3 of the trailer cameras 29,30, 31 are illustrated by dashed triangles in FIGS. 3 and 4. The trailer5 optionally also comprises an obstruction detection system, for exampleparking sensors 32A, 32B, for detecting the presence of obstructions atthe rear of the trailer 5. The image data from the trailer cameras 29,30, 31 and/or obstruction data from the obstruction detection system istransmitted to the vehicle 3 over either a wired connection or awireless communication channel.

The vehicle control system 1 comprises an electronic control unit (ECU)having an electronic processor 33, as shown schematically in FIG. 2. Theprocessor 33 comprises image processing means in the form of an imageprocessing module 33A for analysing the image data. The vehicle cameras9, 10, 11 and the trailer cameras 29, 30, 31 each output image data tothe image processing module 33A for analysis. In use, the imageprocessing module 33A analyses the image data from the vehicle cameras9, 10, 11 to identify the target 25 to determine the current position ofthe trailer 5 in relation to the vehicle 3. In particular, the imageprocessing module determines the current orientation of the trailer 5relative to the vehicle 3. Moreover, the image processing module 33Aanalyses the image data from the trailer cameras 29, 30, 31 to identifyobstructions proximal to the trailer 5. The image processing module 33Acan optionally analyse the image data from the vehicle cameras 9, 10, 11to identify obstructions proximal to the vehicle 3 and trailer 5.

The image processing module 33A is configured to multiplex the imagesfrom the trailer cameras 29, 30, 31 to generate a composite image 35showing a panoramic view to the rear of the trailer 5, as shown in FIG.9. The resulting composite image 35 can be output to a display screen 37to be viewed by the user substantially in real-time. The display screen37 can be provided in an instrument cluster or in an infotainmentconsole. The image data from the vehicle cameras 9, 10, 11 and thetrailer cameras 29, 30, 31 could be combined to provide a plan view ofthe vehicle 3 and the trailer 5 (as if viewed from a position above thevehicle 3 and the trailer 5).

The processor 33 further comprises vehicle/trailer guidance means in theform of a guidance module 33B. The guidance module 33B is provided toassist with guiding the trailer 5 when the vehicle 3 and the trailer 5are being reversed together. In particular, the guidance module 33B isconfigured to output a control signal for controlling the steering angleθ of the front wheels W1, W2 of the vehicle 3 to guide the trailer 5along a target route R. The target route R is generated by the guidancemodule 33B to guide the trailer 5 from its current position to a targetdestination D_(TAR) specified by the user. The target route R isillustrated by a dashed line in FIG. 3 and the path to be followed bythe wheels W1, W2 of the trailer 3 are represented by arcuate lines inFIG. 4.

The vehicle control system 1 comprises a human machine interface (HMI)module 39. The HMI module 39 is coupled to the display screen 37 and isconfigured to superimpose a graphical image 41, representing the targetdestination D_(TAR) of the trailer 5, onto the composite image 35. Inthe present embodiment the graphical image 41 comprises a rectangle 43which represents the footprint of the trailer 5. The graphical image 41is sized to provide a scale representation of the trailer 5 within thecomposite image 35. To provide an accurate representation of the trailer5, the trailer dimensions can be specified by the user and stored in adata file accessible to the HMI module 39. In the present embodiment aportion of the graphical image 41 is semi-transparent to reduceobfuscation of objects in the composite image 35. It will be appreciatedthat the present invention is not limited to the display of a rectangle43 and other graphical images 39 can be used to represent the trailer 5.

The HMI module 39 is coupled to input means 45 in the form of a touchscreen and a rotary dial. The input means 45 can be operated by the userto position the graphical image 41 within the composite image 35. Theuser can thereby position the graphical image 41 to specify the targetdestination D_(TAR) for the trailer 5, typically corresponding to alocation where the trailer 5 is to be parked. The input means 45 canoptionally also enable the user to define the orientation of the trailer5 in relation to the vehicle 3, for example by adjusting the angularorientation of the rectangle 43.

The HMI module 39 performs a scaling operation on the graphical image 41to adjust its size based on its position within the composite image 35,for example to increase/decrease its size in dependence on its virtualposition in relation to the camera generating the video image. Thegraphical image 41 can optionally also be modified to alter itsperspective, for example to simulate foreshortening, as it is movedwithin the composite image 35. The graphical image 41 can therebyprovide an accurate representation of the size of the trailer 5 withinthe composite image 35. The processor 33 could be configured to identifyareas or regions which are unsuitable for positioning the trailer 5. TheHMI module 39 can be configured to represent any such areas as anoverlay on the composite image 35. Alternatively, or in addition, theHMI module 39 can be configured to prevent the graphical image 41 beingmoved to locations identified by the processor 33 as being unsuitablefor positioning the trailer 5. For example, the processor 33 coulddetermine that a region displayed in the composite image 35 isunsuitable due to the detection of one or more obstructions by the imageprocessing module 33A. Alternatively, or in addition, the processor 33could assess one or more terrain parameters, such as incline orgradient, to identify unsuitable regions for the trailer 5. The terrainparameters could be assessed from the image data derived from thevehicle cameras 9, 10, 11 and/or the trailer cameras 29, 30, 31.Alternatively, or in addition, one or more of the following types ofsensor could be employed to monitor the terrain: ultrasonicsensors/cameras, laser scanners and radar. The resulting terrain datacould be used to restrict selection of the target destination D_(TAR);and/or control vehicle operating parameters, for example to engage fourwheel drive or to select a low transfer range; and/or request userconfirmation of the selected target destination D_(TAR).

The guidance module 33B is configured to generate the target route R toguide the trailer 5 from its current location to the target destinationD_(TAR) specified by the user. The target route R defines a targettrailer travel direction T_(TAR) for guiding the trailer 5 from itscurrent position to the target destination D_(TAR). The target route Rcan comprise rectilinear and/or curved sections. The target route R isarranged coincident with a midpoint of the trailer 5 in its currentposition. The current position of the trailer 5 is monitored compared tothe originally calculated target route R. Small deviations are managedwithin the vehicle control system 1. Larger deviations can trigger arecalculation of the target route R. If the target destination D_(TAR)becomes unachievable from the current position, the user is alerted anda corrective manoeuvre is suggested (for example travel forward a shortdistance).

The user positions the graphical image 41 within the composite image 35to define the target destination D_(TAR) of the trailer 5. The guidancemodule 33B determines the target route R between the current trailerposition and the specified target destination D_(TAR). As illustrated inFIG. 5, the vehicle steering angle θ is controlled such that a center ofrotation 49 of the trailer 5 defines a first path 51 which at leastsubstantially matches the target route R. The trailer hitch 19 defines asecond path 53 as the trailer 5 follows the target route R; and a centerof rotation 55 of the vehicle 3 defines a third path 57 as the trailer 5follows the target route R. In an alternate embodiment, the guidancemodule 33B could be configured to generate the second or third paths 53,55 to guide the trailer 5 to the target destination D_(TAR) and tocontrol the vehicle steering angle θ to follow said second or thirdpaths 53, 55. The target route R is a straight line if the targetdestination D_(TAR) is in line with the trailer 5. Otherwise, the targetroute R comprises a curve based on the geometry of the vehicle andtrailer and location of the target destination.

With reference to FIGS. 6A-6E, the guidance module 33B implements ageometric algorithm to generate the target route R. The guidance module33B utilises the angular offset between the current trailer longitudinalaxis X2 and the target trailer longitudinal axis X2 _(TAR); and thelateral offset between the current trailer position and the targetdestination D_(TAR) (measured perpendicular to the trailer longitudinalaxis X2. As shown in FIG. 6A, the algorithm defines a default S-shapedpath 55 (shown in phantom in FIGS. 6B-6E) comprising first and secondcurves A, B. The first curve A defines a first included angle of +45°;and the second curve B defines a second included angle of −45°. Ifrequired, a scaling function (along an X axis and/or a Y axis) isapplied to the S-shaped path 55 to link the actual longitudinal axis X2of the trailer 5 to the target longitudinal axis X2 _(TAR) of thetrailer 5 when it is in the target destination D_(TAR). The guidancemodule 33B can optionally be configured to define a minimum radius ofcurvature for the first and second curves A, B to ensure that the hitchangle φ does not equal or exceed the jack-knife angle.

The S-shaped path 55 is positioned to link the actual longitudinal axisX2 of the trailer 5 to the target longitudinal axis X2 _(TAR). A scalingfunction and/or a rotation function can be applied to the S-shaped path55 depending on the position and/or orientation of the targetdestination D_(TAR) in relation to the current trailer position. TheS-shaped path 55 is then modified by adjusting the included angle ofeither the first curve A or the second curve B in dependence on theangular offset between the actual longitudinal axis X2 and the targetlongitudinal axis X2 _(TAR).

In the present embodiment, the guidance module 33B identifies which ofthe first and second curves A, B opens onto the side of the S-shapedpath 55 to which the target longitudinal axis X2 _(TAR) is oriented. Theguidance module 33B then modifies the included angle of the identifiedcurve A, B corresponding to the angular offset between the actuallongitudinal axis X2 and the target longitudinal axis X2 _(TAR). Thistechnique will now be described with reference to FIGS. 6B-6E.

In the scenario illustrated in FIG. 6B, the target longitudinal axis X2_(TAR) is offset by −45° and is directed to the left side of theS-shaped path 55. Accordingly, the included angle of the first curve A(which opens to the left side of the S-shaped path 55) is reduced by45°. As the pre-defined included angle is +45°, the first curve A iseffectively removed from the S-shaped path 55 leaving only the secondcurve B. The resulting modified curve is defined as the target route R.

In the scenario illustrated in FIG. 6C, the target longitudinal axis X2_(TAR) is offset by −90° and is directed to the left side of theS-shaped path 55. Accordingly, the included angle of the first curve Ais reduced by 90° to define an included angle of −45°, thereby reversingthe curvature direction of the first curve A. The resulting modifiedcurve is defined as the target route R.

In the scenario illustrated in FIG. 6D, the target longitudinal axis X2_(TAR) is offset by +45° and is directed to the right side of theS-shaped path 55. Accordingly, the included angle of the second curve B(which opens to the right side of the S-shaped path 55) is increased by45°. As the pre-defined included angle is −45°, the second curve B iseffectively removed from the S-shaped path 55 leaving only the firstcurve A. The resulting modified curve is defined as the target route R.

In the scenario illustrated in FIG. 6E, the target longitudinal axis X2_(TAR) is offset by +90° and is directed to the right side of theS-shaped path 55. Accordingly, the included angle of the second curve Bis increased. However, to compensate for the lateral offset of thetrailer 5, the second curve B is increased by 45° to 0°, therebyremoving the second curve B. The first curve A is also increased by 45°to 90° (again to compensate for the lateral offset of the targetdestination D_(TAR)). The resulting modified curve is defined as thetarget route R.

In a second process step, the vehicle control system 1 attempts toidentify the presence of any obstructions (denoted generally by thereference numeral 46 in FIGS. 7A and 7B). Typical obstructions includekerbs, walls, vehicles, etc. The vehicle control system 1 can optionallyalso determine terrain parameters, for example to detect a metalledsurface indicating a road; and/or terrain features, for example gradientchanges. As described herein, the obstructions 46 can be identified bythe image processing module 33A and/or other detection systems. Theguidance module 33B modifies the target route R generated in the firstprocess step. By way of example, the guidance module 33B will give ahigher priority to a route which guides the trailer 5 to the targetdestination D_(TAR) whilst remaining on a road than a route whichprovides the shortest achievable path.

With reference to FIGS. 7A and 7B, in order to guide the trailer 5 theguidance module 33B calculates the required vehicle steering angle θ toachieve the appropriate trailer angle δ at intervals x, 2x, 3x . . . nxalong the route R, where x equals half the combined length of thevehicle 3 and the trailer 5. The interval distance x is configurable andcan be reduced, for example to ¼ the combined length of the vehicle 3and the trailer 5 to provide improved accuracy, albeit at the expense ofincreased processing load on the processor 33 The trailer angle δ is theangle between an expected angular position of the trailer 5 at aparticular interval and the position of the trailer 5 before themanoeuvre starts. Once the guidance module 33B has calculated therequired trailer angle δ at the calculating points (defined by the nintervals along the target route R), the trailer angles δ_(n), δ_(n+1)at adjacent calculation points are compared to determine the differencebetween the trailer hitch angles φ_(n), φ_(n+1) at adjacent intervalpoints.

If the hitch angle φ can be achieved between the two calculation points,the guidance module 33B stores the values in memory and, during themanoeuvre, accesses the stored values after each interval to set thenext interval value as the desired hitch angle φ. If the guidance module33B detects a large deviation between the present hitch angle φ and theexpected hitch angle φ it restarts the calculation to avoid failure.

If the hitch angle φ between the two calculation points cannot beachieved (for example based on the maximum steering angle θ of thevehicle and the trailer geometry), the guidance module 33B compares therequired hitch angle φ_(n), φ_(n+1) between first and second intervals xto establish if this hitch angle φ can be achieved while consideringsurrounding conditions. If the comparison of the hitch angle φ_(n),φ_(n+1) between the first and second intervals x is possible, theguidance module 33B stores the values in memory and, during themanoeuvre, accesses the stored values after each interval to set thenext interval value as the desired hitch angle φ. If the guidance module33B fails to achieve the required hitch angle φ for four (4) consecutiveinterval points (i.e. x to 4x), an alternative target route R iscalculated while considering space requirement and the surroundingobstructions 46. If the guidance module 33B is unable to establish aviable alternative target route R, the guidance module 33B calculates analternate position between failure points identified by means of drivingforward in the available space to complete the manoeuvre. During theroute calculation the guidance module 33B determines whether the hitchangle φ change between two intervals can be achieved. If the hitch angleφ cannot be achieved then the calculation needs to check if the hitchangle φ change calculated in alternative routes in two previous and twosubsequent intervals can be achieved. If this fails then the calculationstarts again or requests an initial drive forwards to reduce the rate ofchange of hitch angle. A forward shuffle could also be requestedmid-manoeuvre.

The angular change Ω in the trailer angle δ at intervals along thetarget route R is illustrated in FIG. 7B. The angular change Ω isillustrated with reference to a first time t and a second time t+1, butthe calculation of the required angle change is based on distance ratherthan time.

As described herein, the steering angle θ of the vehicle 3 is controlledto maintain the actual travel direction T_(ACT) of the trailer 5substantially coincident with the target trailer travel directionT_(TAR) during the reversing manoeuvre along said target route R. Theguidance module 33B can control the steering angle θ of the front wheelsW1, W2 to guide the trailer 5 along the target travel direction T_(TAR).

The control algorithm for generating a control signal to guide thevehicle 3 along the target route R will now be described with referenceto FIG. 9. The vehicle 3 has a first longitudinal axis X1 and thetrailer 5 has a second longitudinal axis X2. The angular offset betweenthe first and second longitudinal axes X1, X2 is referred to as thehitch angle φ. During reversing, the trailer 5 travels in a directionT_(ACT) corresponding to the hitch angle φ (unless the hitch angle φexceeds a jack-knife angle for the trailer 5, as described herein).

The image processing module 33A calculates the hitch angle φ withreference to the target 25 and outputs a hitch angle signal to theguidance module 33B. When reversing, the guidance module 33B calculatesthe required steering angle θ based on the following equation:θ_(t+1)=θ_(t)+min(max(k(φ_(req)−φ_(cur)),−α),α)

-   Where: θ_(t+1) and θ_(t) are the steering angles of the vehicle 3 at    frame t+1 and t (auto steering command from the algorithm and    current steering from the CAN respectively);    -   φ_(req) and φ_(cur) are the requested and current hitch angles;    -   α is the maximum steering offset value; and    -   k is a constant multiplier.

The value of the gain k can be calculated based on the relationshipbetween θ and φ, as shown in FIG. 8. When the trailer hitch length Lplus the tow bar offset of the vehicle h is equal to the vehiclewheelbase d, then the relationship between θ and φ is one (1) for smallangles and so the gain k can be set to a value of one (1). The gain kcan therefore be calculated based on the following equation:

$k = \frac{L + h}{d}$

-   Where: L is the hitch length of the trailer 5;    -   h is the tow bar offset of the vehicle 3;    -   d is the wheelbase of the vehicle 3;

The gain k thereby compensates for the fact that longer trailers takelonger to reach the requested hitch angle φ.

The guidance module 33B is configured to calculate a maximum permissiblehitch angle φ_(MAX). If the hitch angle φ exceeds the maximumpermissible hitch angle φ_(MAX) (which in the present embodiment is thejack-knife angle of the trailer 5), it is no longer possible to reducethe hitch angle φ by continuing to reverse (i.e. the trailer 5 hasjack-knifed). If the detected hitch angle φ is equal to or exceeds thecalculated jack-knife angle, the vehicle control system 1 will advisethe user to drive forward until it determines that the trailer angle δat the next interval is achievable while considering space andobstructions. With reference to FIG. 8, the guidance module 33Bcalculates the maximum permissible hitch angle φ_(MAX) by applying thefollowing set of equations:

$R = \frac{d}{\tan(\theta)}$$\phi = {{\cos^{- 1}\left( \frac{{- {Lh}} + {R\sqrt{R^{2} + h^{2} - L^{2}}}}{R^{2} + h^{2}} \right)}\mspace{14mu}{for}\mspace{14mu}{positive}\mspace{14mu}\theta}$$\phi = {{- {\cos^{- 1}\left( \frac{{- {Lh}} - {R\sqrt{R^{2} + h^{2} - L^{2}}}}{R^{2} + h^{2}} \right)}}\mspace{14mu}{for}\mspace{14mu}{negative}\mspace{14mu}\theta}$

-   Where: R is the turning radius;    -   θ is the steering angle of the vehicle 3;    -   d is the wheelbase of the vehicle 3;    -   h is the tow bar offset of the vehicle 3;    -   L is the hitch length of the trailer 5;

The wheelbase d, the tow bar offset h and the maximum steering angleθ_(MAX) of the vehicle 3 are defined for the vehicle 3. The hitch lengthL of the trailer 5 is entered during trailer setup by the user (or canbe determined during a calibration exercise). The guidance module 33Boutputs a maximum hitch angle signal to indicate the maximum permissiblehitch angle φ_(MAX) for the current steering angle θ. The guidancemodule 33B is configured to inhibit the trailer travel direction T_(ACT)to values which are less than the maximum permissible hitch angleφ_(MAX). A minimum radius of curvature of the target route R can bedefined to ensure that the trailer travel direction T_(ACT) is less thanor equal to the maximum permissible hitch angle φ_(MAX).

The guidance module 33B calculates the initial required steering angle θto achieve the desired hitch angle φ, then iteratively calculates therequired steering angle θ and hitch angle φ. In use, the guidance module33B is configured to output a steering control signal operative tocontrol the steering angle θ of the front wheels W1, W2 to adjust thehitch angle φ, thereby modifying the actual trailer travel directionT_(ACT). Specifically, the guidance module 33B adjusts the steeringangle θ (which can be positive or negative in relation to a referencepoint) to increase or decrease the hitch angle φ. The actual trailertravel direction T_(ACT) can thereby be matched to the target trailertravel direction T_(TAR) required to follow the target route R. Thehitch angle signal is updated at least substantially in real time andthe guidance module 33B makes corresponding real time adjustments to thesteering control signal. The guidance module 33B controls the hitchangle φ so that the difference between the actual trailer traveldirection T_(ACT) and the target trailer travel direction T_(TAR) is atleast substantially zero. A tolerance of +/−0.5° between the actualtrailer travel direction T_(ACT) and the target trailer travel directionT_(TAR) provides a good result.

The steering angle control signal is output to an electronic powerassisted steering (EPAS) module 45 to control the angle of a steeringwheel 47 to provide a required steering angle θ for the front wheels W1,W2. The EPAS module 45 automatically adjusts the angular orientation ofthe steering wheel 47 to provide the appropriate steering angle θ at thefront wheels W1, W2 to control the vehicle 3 to match the actual trailertravel direction T_(ACT) with the target trailer travel directionT_(TAR).

In use, the user operates the HMI module 39 to position the graphicalimage 41 at the target destination D_(TAR) for the trailer 5, asillustrated in FIG. 9. Specifically, the user operates the input means45 to guide the graphical image 41 to the desired location on the videoimage 35. The input means 45 can be operated to adjust the positionand/or orientation of the target destination D_(TAR) for the trailer 5.The user then confirms the target destination D_(TAR) for the trailer 5.

The image processing module 33A analyses the image data from the vehiclecameras 9, 10, 11 to identify the target 25 on the trailer 5 and todetermine the current position of the trailer 5 in relation to thevehicle 3. The guidance module 33B then models a target route R for thetrailer 5 from its current position to the target trailer destinationD_(TAR). A vehicle control signal is output by the guidance module 33Bto the EPAS module 45 to adjust the steering angle θ to control thevehicle 3 to match the actual travel direction T_(ACT) of the trailer 5with the target travel direction T_(TAR). The HMI module 39 canoptionally output instructions to prompt the user to select theappropriate drive gear and to operate the vehicle brakes and throttle.The EPAS module 45, in dependence on the vehicle control signal outputfrom the guidance module 33B, then steers the vehicle 3 to guide thetrailer 5 along the target route R. A notification can be output by theHMI module 39 to notify the user when the trailer 5 is in the targetdestination D_(TAR). The vehicle control system 1 can thereby facilitatereversing the trailer 5 to the target destination D_(TAR).

The present invention is applicable to a range of different types oftrailer 5. For example, the trailer 5 can be a caravan, a goods trailer,a flatbed trailer, a van trailer, a livestock trailer and so on.Similarly, the present invention is applicable to a range of differenttypes of vehicles 3. For example, the vehicle 3 can be a motor vehicle,such as an off-road or sports utility vehicle; or a towing engine ortractor for a semi-trailer truck.

The control techniques described herein are a development of thosedescribed in the Applicant's earlier UK patent applications GB1307524.7(filed on 26 Apr. 2013) and GB1307525.4 (filed on 26 Apr. 2013), thecontents of which are incorporated herein in their entirety byreference. Furthermore, the contents of the Applicant's relatedapplication entitled “VEHICLE CONTROL SYSTEM” filed on the same day asthe present application at the UK Intellectual Property Office arehereby incorporated in their entirety into the present application byreference.

It will be appreciated that various changes and modifications can bemade to the vehicle control system 1 described herein without departingfrom the present invention. Rather than specify the target trailerdestination D_(TAR) by positioning the graphical image 41 on a videoimage, the graphical image 41 could be positioned on a static image suchas a grid or mesh representing a predefined region around the vehicle 3.

Furthermore, although the vehicle control system 1 has been describedwith reference to a set of vehicle cameras 9, 10, 11 and a set oftrailer cameras 29, 30, 31, it will be appreciated that a single cameracould be provided on the vehicle 3 and/or the trailer 5. In a furtheralternative, the trailer cameras 29, 30, 31 could be omitted. A set ofparking sensors provided on the trailer 5 could, for example, providenotification to the driver of any obstructions. The hitch angle φ couldbe measured directly, for example by a rotary encoder.

In a further alternative, a video image could be transmitted to thevehicle 3 from a remote camera (for example provided in a cellulartelephone) over a wireless network such as Bluetooth®.

The invention claimed is:
 1. A system for controlling a vehicle to facilitate reversing a trailer coupled to the vehicle, the system comprising a processor configured to: identify permissible target trailer destinations and impermissible target trailer destinations; receive a target trailer destination specified by a user; determine a current trailer position; model a target route from the current trailer position to the user-specified target trailer destination; and output a vehicle control signal for controlling the vehicle to guide the trailer along the target route; wherein the processor inhibits user selection of an impermissible target trailer destination.
 2. The system of claim 1, wherein the target trailer destination comprises location data and/or orientation data.
 3. The system of claim 1, wherein the target route comprises one or more curves joining the current trailer position to the target trailer destination.
 4. The system of claim 3, wherein the vehicle control signal maps a center point of the trailer to the target route.
 5. The system of claim 1, wherein the processor is configured to identify the permissible target trailer destinations based on a detected available space for the trailer.
 6. The system of claim 1, wherein the processor is configured to receive image data from one or more video cameras disposed on the vehicle and/or the trailer.
 7. The system of claim 6, wherein the processor is configured to identify one or more obstructions proximal to the trailer and/or the vehicle.
 8. The system of claim 6, wherein the processor is configured to overlay the target trailer destination and/or a target route for the trailer on a video image from the one or more video cameras.
 9. The system of claim 1, wherein the vehicle control signal comprises a steering control signal for controlling a steering angle of the vehicle.
 10. A vehicle comprising the system of claim
 1. 11. The system of claim 1, wherein the processor is configured to identify the permissible target trailer destinations based on at least one of a maximum permissible hitch angle, and a detected terrain parameter.
 12. A method of controlling a vehicle to facilitate reversing a trailer to a specified target trailer destination, wherein the vehicle comprises a human machine interface (HMI) module, an electronic power assisted steering (EPAS) module, at least one camera, and a control unit having a guidance module and an image processing module, the method comprising: receiving at the control unit a user input via the HMI module that defines a user-specified target trailer destination, wherein the control unit is configured to identify permissible target trailer destinations for positioning the trailer and impermissible target trailer destinations unsuitable for positioning the trailer, the control unit being configured to inhibit user selection of an impermissible target trailer destination; processing image data from the at least one camera via the image processing module to determine a current orientation of the trailer relative to the vehicle; modeling a target route from a current trailer position to the user-specified target trailer destination via the guidance module; and outputting, via the guidance module, a vehicle control signal to the EPAS module for controlling the vehicle to guide the trailer along the target route. 